U.S. Pat. No. 6,128,910 describes a method for diagnosing a refrigeration system for the cooling of air. In the method the physical values of the air, which pass through a heat exchanger of the system, are measured by a sensor arrangement (48), which is part of a measuring unit (44). The measured values are: air temperature, relative humidity of the air and volume flow of the air. By way of the air temperature and the relative humidity of the air an enthalpy change of the air by passage through the heat exchanger is determined. This change together with the volume flow is used to detect decreased air flow and lowered heat transfer, as well as lowered SHR. By way of additional measurements, the cooling medium temperature in the suction duct as well as the temperature of the liquid cooling medium between the condenser and the expansion valve, and the charging of the cooling medium can be investigated.
To explain the invention, in the following a sales cooling chest has been chosen as an example of the refrigeration system. The invention is, however, also useful in the case of other refrigeration systems. In the case of a sales cooling chest, such as for example used in supermarkets to hold cool or frozen products in ready condition for sale, an air flow which forms the first media flow is circulated in an air channel in which an evaporator is arranged. The evaporator is a heat exchanger on one side of which a cooling medium, comprising the second media flow, is moved in a liquid or two phase condition (gas and liquid). When the air is moved over the other side of the evaporator a heat transfer occurs from the air to the cooling medium and the air is cooled. Another example of a heat exchanger is the condenser over which the air is moved to liquefy the cooling medium. In this way heat is extracted from the cooling medium.
In the case of such a refrigeration system one wishes to be able to determine with a certain reliability whether the air stream can circulate in a sufficient mass; that is one wants to determine whether disturbances have appeared. Such disturbances can for example arise in that a fan has failed, in that the evaporator has iced up, in that dirt has accumulated in the air channel or that objects such as sales debris or goods have clogged the air channel and have increased the flow resistance for the air and have thereby hindered the air flow.
Such a fault recognition should most desirably take place before the cooling efficiency of the cooling system has been too strongly lessened. If a fault can first be recognized by an increase in temperature, it can be already too late for the cooled or frozen products; that is a risk exists that these products will have been spoiled. In many cases a disturbance of the air stream long before a damaging of the cooled products occurs means that the refrigeration system is not being operated at its optimum operating point. If therefore a fault has indeed occurred, individual components of the refrigeration system often become overloaded which reduces their service lifetime. This can be easily drawn from the example of fans. If one of several fans fails, the one or more remaining fans thereafter as before drive the necessary air flow through the refrigeration system to create the cooling efficiency. The remaining fans are, however, overloaded. Along with a lessening of the service life of the components, for example the fans, a fault has the disadvantage of an increased energy consumption. The refrigeration system becomes not operating at its optimum operating point. For this reason also the recognition of faults is important.
The invention has as its object the ability to recognize changes in the first media flow as early as possible.